The invention relates to a local communication bus system comprising a serial control bus attached to a plurality of addressable devices, each device including at least one functional element addressable via the bus as a subdevice, the subdevices in the system including a user output subdevice for displaying status information to a user of the system and a first control subdevice for initiating the display of such status information.
The invention further relates to an apparatus for use in such a system, such apparatus including an interface to a serial control bus and being addressable as a device via said bus, the apparatus further including one or more functional elements addressable via the bus as subdevices.
A known serial control bus for interconnecting domestic audio and video apparatuses is the Domestic Digital Bus (D2B) Standardised by the International Electrotechnical Commission (IEC). An apparatus including D2B interface and on screen display (OSD) of status information is available in the United Kingdom in the form of Philips' 2070 colour television receiver. In the known apparatuses, the displayed status information is limited to information on the status within the apparatus itself. While it is known for another apparatus, for example a VCR, to superimpose status messages on its video output for display to the user via a television screen, again the content of the user messages is limited to status within the apparatus initiating that message. Furthermore, and particularly when apparatuses of different manufacturers are used together, there is no guarantee that the on-screen messages of one apparatus will not conflict with those of another, and it is not desirable, for example, for a satellite tuner to superimpose status messages on its video output signal when the latter is being recorded by a VCR.
Another problem that arises in obtaining status information, either in the form of user messages or in machine-readable form for internal control purposes, is that status can change in response to a variety of events. For example, a tape deck in a fast wind or play mode will stop when the end of the tape is reached. While the known bus system allows status to be monitored by polling of devices and subdevices with frequent request messages, the amount of bus traffic (requests and replies) involved in such polling renders it impractical for widespread use in a system of more than a very few subdevices.